Now, terrifying moments in a packed theater. Hundreds traumatized when the roof collapsed during a live performance last night at the historic apollo theater in london. Terry moran is there with the latest. Good morning, terry. Reporter: Good morning, george. An investigation is under way this morning to find out what happened here. What caused the frightening collapse of the ornate plaster ceiling of the apollo theater, that old theater back there. For hundreds of audience members, it was a shocking and surreal night at the theater. Inside the apollo theater today, A WRECK. &-pALL THAT DEBRIS CRASHING DOWN On a packed house, in one terrifying moment last night. 76 people injured, 4 seriously. The wounded carried out on stretchers. Iconic london buses, used as makeshift ambulances. As far as we know, the roof collapsed above us. And I just got a bang on the head. The next thing I know, I was in the foyer. Reporter: It happened during act one of the hit play "the curious incident of the dog in the nighttime." Witnesses said one of the actors shouted, watch out, as the ceiling came down. We heard a creek. And the ceiling, it just slowly -- and the whole thing just collapsed. Just like that. Reporter: This theater, more than 100 years old, the ceiling a grand, heavy plaster design. More than 900-square feet of it came down on that audience. The height of a five-story building. It's been confined to some heavy ornate plastering, typical of what you would expect to find in a theater in the west end of this age. It's from the roof level. Reporter: Two people remain hospitalized this morning. But think about how vulnerable everybody in this place was and how much debris came down, this is an incredibly close call. It is, terry. Now, to the latest on target and the escalating backlash

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